There are multiple automotive, marine and aviation applications where small, low cost millimeterwave (MMW) radar sensors are distributed around a vehicle to provide functions, such as adaptive cruise control, anti-collision warning, brake applications, parking, marine threat detection or marine docking guidance.
Many developers have created low cost MMW sensors, particularly for the automotive marketplace where production numbers can be in the 100,000s. Most use modulation that is either FM/CW or UltraWideband. In the typical application, each sensor provides its own modulation and signal processing in a single package. Adding more sensors requires adding complete radar and signal processing/control systems to each location and then combining data from each in yet another computing platform. This duplicates many functions.
The RF implementation of the MMW Radar subsystems has either been overly complex (frequency multiplication systems) or overly simple with poor RF performance (MMW Oscillator directly connected to an antenna and modulated). Both systems generate very high phase noise and varying modulation characteristics over time and environmental changes.
U.S. Pat. No. 7,324,039 to Boltovets et al. attempts to generate a MMW radar signal by frequency multiplication of an open loop X band Voltage Controlled Oscillator. This choice for FM/CW modulation also directly multiplies any modulation non-linearity and causes phase noise to increase by a factor of 20 Log N where N is the multiplication factor. Both factors significantly degrade the performance of the resulting system.
Overly simple systems that employ a directly modulated MMW VCO to avoid the use of frequency multiplication achieve an overly sensitive VCO that is easily made non-linear by circuit effects, temperature or movement of objects present in the antenna beam.